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non-rectangular (line and circle) clears in canvas
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/* | |
To see a demo of these in use, check out: http://test.getify.com/test-canvas-clear-alt.html | |
Example uses: | |
*/ | |
clearCircle(context,/*x=*/120,/*y=*/80,/*radius=*/60); | |
clearLineSquared(context,/*x1=*/10,/*y1=*/10,/*x2=*/53,/*y2=*/67,/*thickness=*/5); | |
clearLineRounded(context,/*x1=*/15,/*y1=*/100,/*x2=*/90,/*y2=*/170,/*thickness=*/10); | |
clearLineRounded(context,/*x1=*/90,/*y1=*/170,/*x2=*/160,/*y2=*/150,/*thickness=*/10); | |
// code | |
function dist(x1,y1,x2,y2) { | |
x2-=x1; y2-=y1; | |
return Math.sqrt((x2*x2) + (y2*y2)); | |
} | |
function clearCircle(context,x,y,radius) { | |
context.save(); | |
context.beginPath(); | |
context.arc(x, y, radius, 0, 2*Math.PI, true); | |
context.clip(); | |
context.clearRect(x-radius,y-radius,radius*2,radius*2); | |
context.restore(); | |
} | |
function clearLineSquared(context,x1,y1,x2,y2,thickness) { | |
var tmp, length; | |
// swap coordinate pairs if x-coordinates are RTL to make them LTR | |
if (x2 < x1) { | |
tmp = x1; x1 = x2; x2 = tmp; | |
tmp = y1; y1 = y2; y2 = tmp; | |
} | |
length = dist(x1,y1,x2,y2); | |
context.save(); | |
context.translate(x1,y1); | |
context.rotate(Math.atan2(y2-y1,x2-x1)); | |
context.clearRect(0,0,length,thickness); | |
context.restore(); | |
} | |
function clearLineRounded(context,x1,y1,x2,y2,thickness) { | |
if (thickness <= 2) { | |
clearLineSquared(context,x1,y1,x2,y2,thickness); | |
return; | |
} | |
var tmp, half_thickness = thickness / 2, length, | |
PI15 = 1.5 * Math.PI, PI05 = 0.5 * Math.PI | |
; | |
// swap coordinate pairs if x-coordinates are RTL to make them LTR | |
if (x2 < x1) { | |
tmp = x1; x1 = x2; x2 = tmp; | |
tmp = y1; y1 = y2; y2 = tmp; | |
} | |
length = dist(x1,y1,x2,y2); | |
context.save(); | |
context.translate(x1,y1); | |
context.rotate(Math.atan2(y2-y1,x2-x1)); | |
x1 = 0; | |
y1 = 0; | |
x2 = length - 1; | |
y2 = 0; | |
// draw a complex "line" shape with rounded corner caps | |
context.moveTo(x1,y1-half_thickness); | |
context.lineTo(x2,y2-half_thickness); | |
context.arc(x2,y2,half_thickness,PI15,PI05,false); | |
context.lineTo(x1,y1-half_thickness+thickness); | |
context.arc(x1,y1,half_thickness,PI05,PI15,false); | |
context.closePath(); | |
x1 -= half_thickness; | |
y1 -= half_thickness; | |
context.clip(); | |
context.clearRect(x1,y1,length+thickness,thickness); | |
context.restore(); | |
} |
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